Modern telecommunication networks often comprise twisted pair, coaxial, or fiber optic lines terminated by a network unit for converting between signals used in different segments of the network. For example, a distribution network might be terminated by a network unit for converting between signals on a distribution line and signals on a subscriber line. In some applications, such network units may provide an interface for a single subscriber, such as in a fiber-to-the-home application, or provide an interface for a plurality of subscribers, such as in fiber-to-the-curb application. A network unit ordinarily comprises electronic components such as analog components, opto-electronic components, and signal processing components mounted on a circuitry substrate.
In typical applications, a network unit is packaged in a network unit enclosure adapted for use in locations where it may be exposed to environmental conditions. In some applications, the network unit enclosure may be mounted on a telephone pole, on an outside wall of a house, or partially sheltered from the elements in a ventilated cabinet on the ground. When placed in such location, the network unit enclosure may be exposed to environmental conditions, particularly to humidity and airborne contaminants such as spores and salt, which require the use of an enclosure with special structural features to avoid the possible deleterious effects of such environmental conditions on the components of the unit. The presence of a high level of humidity and contaminants can cause many known problems such as signal leakage, corrosion, mildew, and dendritic growth of conductor material. These problems can have deleterious effects on electronic components of a network unit and be the cause of intermittent or permanent failure of the network unit, resulting in loss of service to subscribers and expenditures in repair or replacement of the network unit. In network units comprising opto-electronic components, humidity and contaminants may also cause a deterioration of optical signals, in particular when less expensive opto-electronic components in non-hermetically sealed packages are used.
A known approach for avoiding the problems caused by humidity and contaminants in a network unit is to provide a hermetically sealed unit enclosure using a metal box sealed in a dry atmosphere using a cover soldered or welded along a periphery and using hermetically sealed bulkhead connectors for input and output signals, and for providing power to the unit. While such a construction may be highly effective in ensuring the absence of humidity within the unit enclosure, the cost of the hermetically sealed bulkhead connectors and the cost of assembling a unit with a soldered or welded cover may be prohibitive in many cost sensitive applications. In optical network units, the use of an optical connector may also involve a degradation of optical signal power due to imperfect alignment of optical conductors or to the presence of contaminants at the interface between optical conductors.
Accordingly, the present invention seeks to provide a network unit enclosure which is adapted for exposure to humidity and airborne contaminants and which may contribute in providing an advantageously cost-effective network implementation.